Heat pump unit and the control method thereof

ABSTRACT

A heat pump unit and methods for operating the heat pump unit are provided. The heat pump unit includes a compressor (101), a throttling device (107), a first heat exchanger (104), a second heat exchanger (102), a third heat exchanger (103) and a mid-pressure tank (110). The heat pump unit operates in multiple run modes and switches between the run modes without shutdown. The first heat exchanger or the second heat exchanger is capable of acting as a condenser in the multiple run modes. When switching from a pre-switching run mode to a post-switching run mode, a control device determines whether to perform a pressure release operation to the first heat exchanger or the second heat exchanger.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of and priority to Chinese PatentApplication No. 201710938025X entitled “Heat Pump Unit and The ControlMethod Thereof,” filed Sep. 30, 2017, and Chinese Patent Application No.2018111137608 entitled “Heat Pump Unit and The Method for Control theHeat Pump Unit,” filed Sep. 25, 2018, which are hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present application relates to the field of heat pumps, and inparticular relates to a heat pump unit (or a heat pump system)applicable to the application scenario where there are demands on bothcold and heat, and the control method thereof.

BACKGROUND

A heat pump unit comprises a compressor, a throttling device and atleast two heat exchangers, the compressor, the throttling device and theat least two heat exchangers form a refrigerant circulation system, andheat is exchanged with the work end (such as water) via the heatexchangers so that heat of condensation can be utilized for heatrecovery heating while cooling the working end. The heat pump unit iscapable of running in multiple modes and being switched between themultiple modes.

When the running mode of the heat pump unit is switched, it may benecessary to change the flow direction of the refrigerant in thecirculation system. In this case, the compressor may first be stopped,the pressure of the heat exchanger (i.e., the heat exchanger acting as acondenser) on the high-pressure side of the circulation system isreleased after a period of time, and then the heat exchanger is switchedto the low-pressure side. The inventors of the present disclosure foundthat the existing heat pump unit cannot be switched between the workingmodes in time. In addition, the pressure in the circulation systemfluctuates greatly and impacts the pipelines greatly at the time of modeswitching. Therefore, the noise and vibration levels are so high thatthe stability and the level of comfort associated with the heat pumpunit is reduced. Especially when defrosting and drainage are necessaryfor the heat exchangers, the shutdown and pressure release time evenexceeds the defrosting and drainage time such that the workingefficiency of the heat pump unit is greatly affected.

Furthermore, it may be necessary to provide a plurality of four-wayreversing valves or three-way reversing valves in a multifunctional heatpump unit so as to change directions for the compressor and thethrottling device. Thus, the connection structures of the pipelines arecomplicated, the energy efficiency of the system is low, the risk of arefrigerant leakage is very high, and a complicated control method maybe required to switch and regulate multiple functions.

To solve the above-mentioned problems, at least one objective of thepresent application is to provide a heat pump unit having multiplefunctions and performing a free switching between the multiple functionsconveniently, smoothly and efficiently.

SUMMARY

One implementation of the present disclosure is a heat pump unit. Theheat pump unit includes a compressor having a suction end and an exhaustend; a throttling device having an inlet end and an outlet end; a firstheat exchanger, a second heat exchanger, and a third heat exchanger, thefirst heat exchanger having a first port and a second port, the secondheat exchanger having a first port and a second port, and the third heatexchanger having a first port and a second port; and a mid-pressure tankbeing provided with a mid-pressure tank first inlet. The first port ofthe first heat exchanger and the first port of the second heat exchangerare controllably fluidly connected to the suction end of the compressorand controllably fluidly connected to the exhaust end of the compressor.The first port of the third heat exchanger is fluidly connected to thesuction end of the compressor. The second port of the first heatexchanger and the second port of the second heat exchanger arecontrollably fluidly connected to the inlet end of the throttlingdevice, controllably fluidly connected to the outlet end of thethrottling device, and controllably fluidly connected to themid-pressure tank first inlet. The second port of the third heatexchanger is controllably fluidly connected to the outlet end of thethrottling device.

The heat pump unit can further include a four-way valve having a firstinterface, a second interface, a third interface, and a fourthinterface. The first port of the first heat exchanger is connected tothe second interface of the four-way valve, the first port of the secondheat exchanger is connected to the fourth interface of the four-wayvalve, the suction end of the compressor is connected to the firstinterface of the four-way valve, and the exhaust end of the compressoris connected to the third interface of the four-way valve.

The heat pump unit can further include a throttling-device-inlet-sidecontrol valve group including a first valve and a second valve. Thesecond port of the first heat exchanger and the second port of thesecond heat exchanger can be controllably fluidly connected to the inletend of the throttling device via the first valve and the second valve ofthe throttling-device-inlet-side control valve group, respectively. Theheat pump unit can further comprise a throttling-device-outlet-sidecontrol valve group including a first valve, a second valve and a thirdvalve. The second port of the first heat exchanger and the second portof the second heat exchanger can be controllably fluidly connected tothe outlet end of the throttling device via the first valve and the asecond valve of the throttling-device-outlet-side control valve group,respectively. The second port of the third heat exchanger can becontrollably fluidly connected to the outlet end of the throttlingdevice via the third valve of the throttling-device-outlet-side controlvalve group.

The mid-pressure tank can be provided with a mid-pressure first outlet.The mid-pressure first outlet can be controllably fluidly connected tothe outlet end of the throttling device. The heat pump unit can furthercomprise a mid-pressure tank first inlet control valve group including afirst valve and a second valve. The second port of the first heatexchanger and the second port of the second heat exchanger can becontrollably fluidly connected to the mid-pressure tank first inlet viathe first valve and the second valve of the mid-pressure tank firstinlet control valve group, respectively. The heat pump unit can furthercomprise a mid-pressure tank first outlet control. The mid-pressurefirst outlet can be controllably fluidly connected to the outlet end ofthe throttling device via the mid-pressure tank first outlet controlvalve.

The heat pump unit can further include a mid-pressure tankpressure-increasing control valve and a mid-pressure tankpressure-reducing control valve. The mid-pressure tank can be providedwith a mid-pressure tank second inlet and a mid-pressure tank secondoutlet. The mid-pressure tank second inlet can be connected to the fluidpath between the exhaust end of the compressor and the four-way valvevia the mid-pressure tank pressure-increasing control valve. Themid-pressure tank second outlet can be connected to the suction end ofthe compressor via the mid-pressure tank pressure-reducing controlvalve.

The mid-pressure tank first inlet control valve group further caninclude a first one-way valve and a second one-way valve. The firstone-way valve can be connected between the first valve of themid-pressure tank first inlet control valve group and the mid-pressuretank first inlet. The second one-way valve can be connected between thesecond valve of the mid-pressure tank first inlet control valve groupand the mid-pressure tank first inlet.

The first valve and the second valve of the throttling-device-inlet-sidecontrol valve group can be one-way valves. The first heat exchanger andthe third heat exchanger can be connected to a first water supply andreturn pipe and a second water supply and return pipe, respectively.

The heat pump unit can further include a control device. The four-wayvalve, the throttling-device-outlet-side control valve group, themid-pressure tank first inlet control valve group, the mid-pressure tankfirst outlet control valve, the mid-pressure tank pressure-increasingcontrol valve and the mid-pressure tank pressure-reducing control valvecan be connected to and controlled by the control device.

The heat pump unit can be configured such that the heat pump unit canrun in multiple modes and can be switched between the multiple modes bycontrolling the flow path of the refrigerant through the compressor, thethrottling device and the first heat exchanger, the second heatexchanger and the third heat exchanger. High-pressure refrigerant fromany of the first heat exchanger and the second heat exchanger which needpressure releasing at the time of mode switching can be received by themid-pressure tank.

Another implementation of the present disclosure is a method forcontrolling a heat pump unit. The heat pump unit includes a compressor,a throttling device, a first heat exchanger, a second heat exchanger, athird heat exchanger, and a mid-pressure tank. The heat pump unit iscapable of running in multiple modes and the first heat exchanger or thesecond heat exchanger is capable of acting as a condenser in themultiple modes. The method includes determining whether it is desired toperform a pressure release operation to the first heat exchanger or thesecond heat exchanger when it is desired to switch the run mode of theheat pump unit from a pre-switching run mode to a post-switching runmode. The method further includes maintaining the pre-switching run modeand performing Operation 1 responsive to a determination that it isdesired to perform the pressure release operation to the first heatexchanger, wherein Operation 1 comprises fluidly connecting the firstheat exchanger to a first inlet of the mid-pressure tank so as todischarge the refrigerant from the first heat exchanger to themid-pressure tank; or maintaining the pre-switching run mode andperforming Operation 2 responsive to a determination that it is desiredto perform the pressure release operation to the second heat exchanger,wherein Operation 1 comprises fluidly connecting the second heatexchanger to the first inlet of the mid-pressure tank so as to dischargethe refrigerant from the second heat exchanger to the mid-pressure tank.

The method can further include performing Operation 3, wherein Operation3 comprises disconnecting the first heat exchanger from the first inletof the mid-pressure tank after a first predetermined amount of time haselapsed since Operation 1 is performed. The method can further includeperforming Operation 4, wherein Operation 4 comprises disconnecting thesecond heat exchanger from the first inlet of the mid-pressure tankafter a second predetermined amount of time has elapsed since Operation2 is performed.

The method can further include starting the post-switching run mode andending the pre-switching run mode after Operation 3 or Operation 4 isperformed.

The method can further include performing Operation 5 responsive to adetermination that it is desired to supplement refrigerant to therefrigerant circulation loop of the post-switching run mode after thepost-switching run mode is started, wherein Operation 5 comprisesfluidly connecting a first outlet of the mid-pressure tank to an outletend of the throttling device.

The method can further include fluidly connecting a second inlet of themid-pressure tank to an exhaust end of the compressor so as to increasethe pressure in the mid-pressure tank responsive to a determination thatthe pressure in the mid-pressure tank is below a first predeterminedpressure value during performing Operation 5.

The method can further include fluidly connecting a second outlet of themid-pressure tank to a suction end of the compressor so as to reduce thepressure in the mid-pressure tank responsive to a determination that thepressure in the mid-pressure tank is above a second predeterminedpressure value during Operation 1 or Operation 2.

The step of determining whether it is desired to perform a pressurerelease operation to the first heat exchanger or the second heatexchanger can include determining that it is desired to perform thepressure release operation to the first heat exchanger or the secondheat exchanger when the first heat exchanger or the second heatexchanger acting as a condenser in the pre-switching run mode does notact as a condenser in the post-switching run mode.

The multiple modes can include a cooling only mode, a heating only mode,a cooling plus heating mode, and a defrosting mode. The first heatexchanger and the third heat exchanger can be connected to a first watersupply and return pipe and a second water supply and return pipe,respectively.

The compressor, the throttling device, the second heat exchanger and thethird heat exchanger can be in a refrigerant circulation loop when theheat pump unit runs in the cooling only mode, wherein the second heatexchanger acts as a condenser in the cooling only mode. The compressor,the throttling device, the first heat exchanger and the second heatexchanger can be in a refrigerant circulation loop when the heat pumpunit runs in the heating only mode, wherein the first heat exchangeracts as a condenser in the heating only mode. The compressor, thethrottling device, the first heat exchanger and the third heat exchangercan be in a refrigerant circulation loop when the heat pump unit runs inthe cooling plus heating mode, wherein the first heat exchanger acts asa condenser in the cooling plus heating mode. The compressor, thethrottling device, the first heat exchanger and the second heatexchanger can be in a refrigerant circulation loop when the heat pumpunit runs in the defrosting mode, wherein the second heat exchanger actsas a condenser in the defrosting mode.

The step of determining whether it is desired to perform a pressurerelease operation to the first heat exchanger or the second heatexchanger can include determining that it is desired to perform thepressure release operation to the second heat exchanger if thepre-switching run mode is the cooling only mode while the post-switchingrun mode is the heating only mode or the cooling plus heating mode;determining that it is desired to perform the pressure release operationto the first heat exchanger when the pre-switching run mode is theheating only mode while the post-switching run mode is the cooling onlymode or the defrosting mode; determining that it is desired to performthe pressure release operation to the first heat exchanger when thepre-switching run mode is the cooling plus heating mode while thepost-switching run mode is the cooling only mode; or determining that itis desired to perform the pressure release operation to the second heatexchanger when the pre-switching run mode is the defrosting mode whilethe post-switching run mode is the heating only mode.

By using the mid-pressure tank to receive the high-pressure refrigerantfrom the heat exchanger, the heat pump unit of the present disclosurecan be capable of switching between multiple modes in time, without anyshutdown. Thus, the time waiting for the heat exchanger to release thepressure is reduced and the switching efficiency can be improved.Therefore, not only the heat pump unit of the present disclosure canrealize multiple modes, such as cooling only, heating only, cooling plusheating, and defrosting, but also the working state of the heat pumpunit can flexibly be regulated according to the requirements for theworking condition. Thus, the cooling capacity and heating capacity ofthe heat pump unit can be regulated to satisfy the requirements for theworking condition. In addition, the pipeline connections of the heatpump unit of the present application can be simple, no gas-liquidseparator or liquid storage needs to be provided separately, thestructure is compact, the risk of a refrigerant leakage is lowered, andthe reliability of the heat pump unit is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a heat pump unit, according to anembodiment of the present disclosure;

FIG. 2A is a block diagram of a control device for the heat pump unit ofFIG. 1, according to some embodiments;

FIG. 2B is a block diagram of a control device for the heat pump unit ofFIG. 1, according to some embodiments;

FIG. 2C is a block diagram of a control device for the heat pump unit ofFIG. 1, according to some embodiments;

FIG. 3A is a block diagram illustrating the refrigerant circulationloops of the heat pump unit of FIG. 1 operating in the cooling onlymode, according to some embodiments;

FIG. 3B is a block diagram illustrating the refrigerant circulationloops of the heat pump unit of FIG. 1 operating in the heating onlymode, according to some embodiments;

FIG. 3C is a block diagram illustrating the refrigerant circulationloops of the heat pump unit of FIG. 1 operating in the cooling plusheating mode, according to some embodiments;

FIG. 3D is a block diagram illustrating the refrigerant circulationloops of the heat pump unit of FIG. 1 operating in the defrosting mode,according to some embodiments;

FIG. 4 is a process flow diagram illustrating a method of switching therun mode of the heat pump unit of FIG. 1, according to some embodiments;

FIG. 5A is a block diagram illustrating the flow path of refrigerantwhen switching the run mode of the heat pump unit of FIG. 1 from acooling mode to a cooling plus heating mode, according to someembodiments;

FIG. 5B is a block diagram illustrating the flow path of refrigerantwhen performing a refrigerant supplement operation to the refrigerantcirculation loop of the heat pump unit of FIG. 1 running in the coolingplus heating mode, according to some embodiments;

FIG. 6 is a block diagram of a heat pump unit according to anotherembodiment of the present disclosure.

DETAILED DESCRIPTION

The following will describe various specific implementation modes of thepresent application by reference to the drawings which constitute a partof the present description. It should be understood that although theterms indicating directions, such as “before”, “behind”, “above”,“below”, “left”, and “right” are used to describe various exemplifiedstructural parts and components in the present application, these termsare just used for the convenience of illustrations and are determinedbased on the exemplified directions in the drawings. Since theembodiments disclosed in the present application can be set in differentdirections, these terms indicating directions are only used asillustrations, instead of restrictions.

FIG. 1 is a block diagram of a heat pump unit according to an embodimentof the present disclosure. As shown in FIG. 1, the heat pump unit of thepresent disclosure comprises a compressor 101, a throttling device 107,a first heat exchanger 104, a second heat exchanger 102, a third heatexchanger 103, a mid-pressure tank 110, a four-way valve 120, and aplurality of other valves that will be introduced below. The connectinglines among the components (including the compressor 101, the throttlingdevice 107, the first heat exchanger 104, the second heat exchanger 102,the third heat exchanger 103, the mid-pressure tank 110, the four-wayvalve 120, and the plurality of other valves) of FIG. 1 representsconnecting pipelines. The compressor 101 has a suction end 106 and anexhaust end 105, and the suction end 106 and the exhaust end 105 arerespectively connected to the four-way valve 120. The compressor 101allows one-way flow of fluid from the suction end 106 to the exhaust end105 thereof. The throttling device 107 has an inlet end 108 and anoutlet end 109, and allows one-way flow of fluid from the inlet end 108to the outlet end 109 thereof. In other embodiments, the four-way valve120 can be replaced by other valves or valve groups. The four-way valve120 shown in FIG. 1 has four interfaces, including a first interface120.1, a second interface 120.2, a third interface 120.3, and a fourthinterface 120.4. The first interface 120.1 is connected to the suctionend 106 of the compressor 101, the third interface 120.3 is connected tothe exhaust end 105 of the compressor 101, the second interface 120.2 isconnected to the first heat exchanger 104, and the fourth interface120.4 is connected to the second heat exchanger 102.

If the third interface 120.3 of the four-way valve 120 is connected tothe second interface 120.2 and the first interface 120.1 is connected tothe fourth interface 120.4, the exhaust end 105 of the compressor 101 isfluidly connected to the first heat exchanger 104 and the suction end106 of the compressor 101 is fluidly connected to the second heatexchanger 102. In this way, the first heat exchanger 104 is capable ofacting as a condenser located on the high-pressure side of the heat pumpunit, while the second heat exchanger 102 is capable of being located onthe low-pressure side of the heat pump unit.

If the third interface 120.3 of the four-way valve 120 is connected tothe fourth interface 120.4 and the first interface 120.1 is connected tothe second interface 120.2, the exhaust end 105 of the compressor 101 isfluidly connected to the second heat exchanger 102 and the suction end106 of the compressor 101 is fluidly connected to the first heatexchanger 104. In this way, the second heat exchanger 102 is capable ofacting as a condenser located on the high-pressure side of the heat pumpunit, while the first heat exchanger 104 is capable of being located onthe low-pressure side of the heat pump unit.

As shown in FIG. 1, the heat pump unit further comprises a third heatexchanger 103, and the third heat exchanger 103 is fluidly connected tothe suction end 106 of the compressor 101. Therefore, the third heatexchanger 103 may be located on the low-pressure side of the heat pumpunit and may not act as a condenser.

Still as shown in FIG. 1, the first heat exchanger 104, the second heatexchanger 102 and the third heat exchanger 103 each have at least twoports, wherein the first port 116.1 of the first heat exchanger 104 andthe first port 121.1 of the second heat exchanger 102 are configured toconnect to the four-way valve 120, and the first port 123.1 of the thirdheat exchanger 103 is configured to connect to the suction end 106 ofthe compressor 101. The heat pump unit further comprises athrottling-device-inlet-side control valve group 115.1,115.2 and athrottling-device-outlet-side control valve group 118.1,118.2,118.3.

The first heat exchanger 104 further has a second port 116.2. The secondport 116.2 is fluidly connected to the inlet end 108 of the throttlingdevice 107 via a first valve 115.1 of the throttling-device-inlet-sidecontrol valve group and the second port 116.2 is fluidly connected tothe outlet end 109 of the throttling device 107 via a first valve 118.1of the throttling-device-outlet-side control valve group, so that thesecond port 116.2 can act as not only the inlet of the first heatexchanger 104 to receive the refrigerant flowing out of the outlet end109 of the throttling device 107, but also the outlet of the first heatexchanger 104 to supply the refrigerant to the inlet end 108 of thethrottling device 107. Therefore, the first heat exchanger 104 allowscontrollable two-way flow of fluid from the first port 116.1 to thesecond port 116.2 thereof or from the second port 116.2 to the firstport 116.1 thereof.

Similar to the first heat exchanger 104, the second heat exchanger 102also has a second port 121.2. The second port 121.2 is fluidly connectedto the inlet end 108 of the throttling device 107 via a second valve115.2 of the throttling-device-inlet-side control valve group and isfluidly connected to the outlet end 109 of the throttling device 107 viaa second valve 118.2 of the throttling-device-outlet-side control valvegroup. Therefore, the second heat exchanger 102 allows controllabletwo-way flow of fluid from the first port 121.1 to the second port 121.2thereof or from the second port 121.2 to the first port 121.1 thereof.

The third heat exchanger 103 also has a second port 123.2, but thesecond port 123.2 of the third heat exchanger 103 is only fluidlyconnected to the outlet end 109 of the throttling device 107 via a thirdvalve 118.3 of the throttling-device-outlet-side control valve group.

In the embodiment shown in FIG. 1, the throttling device 107 is anexpansion valve, the high-pressure refrigerant goes from the inlet end108 into the expansion valve 107 and is changed into a low-pressurerefrigerant, and the low-pressure refrigerant is then discharged fromthe outlet end 109. Thus, in order to let the refrigerant in the firstheat exchanger 104 and the second heat exchanger 102 controllably flowto the inlet end 108 of the throttling device 107, the first valve 115.1and the second valve 115.2 of the throttling-device-inlet-side controlvalve group can be solenoid valves or one-way valves. For example, thefirst valve 115.1 and the second valve 115.2 of thethrottling-device-inlet-side control valve group in the embodiment shownin FIG. 1 are one-way valves so that much more cost can be saved. Therefrigerant in the first heat exchanger 104 can flow to the inlet end108 of the throttling device 107 when the one-way valve 115.1 is opened,and the refrigerant in the second heat exchanger 102 can flow to theinlet end 108 of the throttling device 107 when the one-way valve 115.2is opened.

The one-way valves are automatically opened and closed due to thepressure difference across the one-way valves without the need of beingcontrolled by the control device 230 as shown in FIG. 2A. However,according to the present disclosure, the first valve 115.1 and thesecond valve 115.2 of the throttling-device-inlet-side control valvegroup can also be solenoid valves which are connected to and controlledby the control device 230 as shown in FIG. 2A. The first valve 118.1,the second valve 118.2 and the third valve 118.3 of thethrottling-device-outlet-side control valve group can be solenoidvalves, so that the refrigerant flowing out of the outlet end 109 of thethrottling device 107 can controllably flow into the required heatexchanger(s). For example, if the first valve 118.1 of thethrottling-device-outlet-side control valve group is opened and thesecond valve 118.2 and the third valve 118.3 of thethrottling-device-outlet-side control valve group are closed, therefrigerant flowing out of the outlet end 109 of the throttling device107 can flow into the first heat exchanger 104.

The first heat exchanger 104, the second heat exchanger 102 and thethird heat exchanger 103 as mentioned above can be different types ofheat exchangers, for example, air heat exchangers exchanging heat withair or waterside heat exchangers exchanging heat with water. As anexemplified embodiment, the second heat exchanger 102 is an air heatexchanger not connected to the working end, while the first heatexchanger 104 and the third heat exchanger 103 are waterside heatexchangers and are respectively connected to first water supply andreturn pipe 111.1 and second water supply and return pipe 111.2 so thatthe heat exchangers can supply the heating load or cooling load requiredon the user side when exchanging heat. As another example, the heat pumpunit of the present application can include more than three heatexchangers.

Still as shown in FIG. 1, the heat pump unit further comprises amid-pressure tank 110. The mid-pressure tank 110 is a container used tostore the refrigerant. The refrigerant can be a refrigerant liquid, or arefrigerant gas, or a mixture of the gas and liquid of a refrigerant.The mid-pressure tank 110 has a mid-pressure tank first inlet 112 and amid-pressure tank first outlet 128, wherein the mid-pressure tank firstinlet 112 is fluidly connected to the heat exchangers (i.e., the firstheat exchanger 104 and the second heat exchanger 102) which are capableof acting as condensers via a mid-pressure tank first inlet controlvalve group 113.1, 113.2.

In the embodiment shown in FIG. 1, the mid-pressure tank first inlet 112is respectively fluidly connected to the second port 116.2 of first heatexchanger 104 and the second port 121.2 of the second heat exchanger 102via a first valve 113.1 and a second valve 113.2 of the mid-pressuretank first inlet control valve group. As an example, the mid-pressuretank first inlet 112 is connected to the fluid path between the firstvalve 115.1 of the throttling-device-inlet-side control valve group andthe inlet end 108 of the throttling device 107 via the first valve 113.1of the mid-pressure tank first inlet control valve group and isconnected to the fluid path between the second valve 115.2 of thethrottling-device-inlet-side control valve group and the inlet end 108of the throttling device 107 via the second valve 113.2 of themid-pressure tank first inlet control valve group. Thus, thehigh-pressure refrigerant in the first heat exchanger 104 and the secondheat exchanger 102 can flow into the mid-pressure tank 110 bycontrolling the throttling-device-inlet-side control valve group 115.1,115.2 and the mid-pressure tank first inlet control valve group 113.1,113.2. As another example, there can be a plurality of shownmid-pressure tank first inlets 112 and each inlet is respectivelyfluidly connected to the heat exchanger which is capable of acting as acondenser via its corresponding first inlet control valve. In anotherembodiment, the mid-pressure tank first inlet control valve group isprovided with only one valve through which the mid-pressure tank firstinlet 112 is connected to the inlet end 108 of the throttling device107.

In the mid-pressure tank 110 shown in FIG. 1, the mid-pressure tankfirst outlet 128 is fluidly connected to the low-pressure side of therunning heat pump unit via a mid-pressure tank first outlet controlvalve 114, and thus the refrigerant in the mid-pressure tank 110 canflow into the refrigerant circulation loop to supplement refrigerant tothe refrigerant circulation loop. The mid-pressure tank first outlet 128is fluidly connected to the second port 116.2 of the first heatexchanger 104, the second port 121.2 of the second heat exchanger 102,and the second port 123.2 of the third heat exchanger 103 via themid-pressure tank first outlet control valve 114. To improve the runningstability of the heat pump unit, the mid-pressure tank first outletcontrol valve 114 can be an expansion valve to ensure that therefrigerant flowing out of the mid-pressure tank first outlet 128 can bechanged into a low-pressure refrigerant and then the low-pressurerefrigerant flows into the low-pressure side of the running heat pumpunit. As an example, the mid-pressure tank first outlet 128 is fluidlyconnected to the outlet end 109 of the throttling device 107 via themid-pressure tank first outlet control valve 114. The mid-pressure tankfirst inlet 112 and the mid-pressure tank first outlet 128 are mainlyused for delivery of the refrigerant liquid such that they are providedat the bottom of the mid-pressure tank 110.

The heat pump unit further comprises a mid-pressure tankpressure-increasing control valve 135 and a mid-pressure tankpressure-reducing control valve 136. The mid-pressure tank 110 isfurther provided with a mid-pressure tank second inlet 181 and amid-pressure tank second outlet 182. As an example, the mid-pressuretank second inlet 181 is connected to the fluid path between the exhaustend 105 of the compressor 101 and the four-way valve 120 via themid-pressure tank pressure-increasing control valve 135, and themid-pressure tank second outlet 182 is connected to the suction end 106of the compressor 101 via the mid-pressure tank pressure-reducingcontrol valve 136. The mid-pressure tank first inlet 112 and themid-pressure tank first outlet 128 are mainly used for delivery of therefrigerant gas such that they are provided at the top of themid-pressure tank 110.

The mid-pressure tank 110 receives the high-pressure refrigerantdischarged from the heat exchangers which are capable of acting ascondensers via the mid-pressure tank first inlet 112 so that therefrigerant and pressure in the heat exchangers are reduced but therefrigerant and pressure in the mid-pressure tank 110 are increased. Themid-pressure tank 110 can also supplement a refrigerant to therefrigerant circulation loop of the heat pump unit through themid-pressure tank first outlet 128. If the pressure is too high in themid-pressure tank 110, the pressure can be reduced by delivery of therefrigerant gas in the mid-pressure tank 110 to the suction end 106 ofthe compressor 101 by opening the mid-pressure tank pressure-reducingcontrol valve 136. If the pressure in the mid-pressure tank 110 is toolow, the pressure can be increased by delivery of the high-pressurerefrigerant gas from the exhaust end 105 of the compressor 101 to themid-pressure tank 110 by opening the mid-pressure tankpressure-increasing control valve 135. Thus, the pressure in themid-pressure tank 110 can be maintained within a desired range.

To further guarantee the flow direction of the fluid in the mid-pressuretank 110, as an example, a first one-way valve 125.1 can be providedbetween the first valve 113.1 of the mid-pressure tank first inletcontrol valve group and the mid-pressure tank first inlet 112, and asecond one-way valve 125.2 can be provided between the second valve113.2 of the mid-pressure tank first inlet control valve group and themid-pressure tank first inlet 112. The first one-way valve 125.1 will beautomatically opened when the first valve 113.1 of the mid-pressure tankfirst inlet control valve group is opened, and the second one-way valve125.2 will be automatically opened when the second valve 113.2 of themid-pressure tank first inlet control valve group is opened. A one-wayvalve (not shown) can also be provided in the downstream fluid path ofthe mid-pressure tank first outlet control valve 114.

Still as shown in FIG. 1, a pressure sensor 161 is provided in themid-pressure tank 110 for detecting the pressure in the mid-pressuretank 110. Pressure sensors 164, 162, and 163 are provided in the firstheat exchanger 104, the second heat exchanger 102 and the third heatexchanger 103, respectively, for detecting the pressure therein.

The heat pump unit further comprises a control device 230 (as shown inFIG. 2), and all the pressure sensors and control valves in FIG. 1 areconnected to the control device 230. FIGS. 2A, 2B, and 2C are blockdiagrams for the control device 230 of the heat pump unit as shown inFIG. 1. As shown in FIG. 2A, the control device 230 comprises a bus 242,a processor 244, an input interface 248, an output interface 252 and amemory 254 in which programs 256 and data 257 are stored. The processor244, the input interface 248, the output interface 252 and the memory254 are communicatively connected to the bus 242 so that the processor244 can control the operation of the input interface 248, the outletinterface 252 and the memory 254. Specifically, the memory 254 isconfigured for storing the programs 256, instructions and data 257, theprocessor 244 can read the programs 256, instructions and data 257 fromthe memory 254 and can write data into the memory 254.

As shown in FIG. 2B, the output interface 252 is connected through theconnections 238 (238.1, 238.2, 238.3 . . . 238.9) to all the controlvalves in FIG. 1, including the first valve 113.1 and second valve 113.2of the mid-pressure tank first inlet control valve group, themid-pressure tank first outlet control valve 114, the mid-pressure tankpressure-increasing control valve 135, the mid-pressure tankpressure-reducing control valve 136, the first valve 118.1, the secondvalve 118.2 and the third valve 118.3 of thethrottling-device-outlet-side control valve group, and the four-wayvalve 120.

As shown in FIG. 2C, the input interface 248 is connected through theconnections 246.2, 246.3, 246.4, and 246.5 to the pressure sensors 161,162, 163, and 164, respectively, and receive through the connection246.1 operation requests to the heat pump unit and other operationparameters. The processor 244 can control the operation of the heat pumpunit of the present disclosure by performing reading the programs andthe instructions via the memory 254.

More specifically, the control device 230 can receive the operationrequests from the heat pump unit (for example, the requests sending froma control panel), the operation parameters sending from the pressuresensors as shown in FIG. 1 and other operation parameters of the heatpump unit via the input interface 248, and send control signals via theoutput interface 252 to the control valves in FIG. 1. By controlling thecontrol valves in FIG. 1, the heat pump unit is capable of running inmultiple modes and being switched between the multiple modes.

FIGS. 3A-3D illustrate the refrigerant circulation loops of the heatpump unit of FIG. 1 running in four modes, respectively, wherein thearrows indicate the flow directions and flow paths of the refrigerant.FIG. 3A illustrates the refrigerant circulation loop in a cooling onlymode (Mode 1), FIG. 3B illustrates the refrigerant circulation loop in aheating only mode (Mode 2), FIG. 3C illustrates the refrigerantcirculation loop in a cooling plus heating mode (Mode 3), while FIG. 3Dillustrates the refrigerant circulation loop in a defrosting mode (Mode4).

Table 1 lists the status of the first valve 118.1, the second valve118.2, and the third valve 118.3 of the throttling-device-outlet-sidecontrol valve group, and the four-way valve 120 for the multiple modesof the heat pump unit. Table 1 can be stored in the storage 254 as shownin FIG. 2A.

TABLE 1 Status of Valves for Various Heat Pump Unit Modes Four-way valveThrottling-device-outlet-side control valve Mode 120 118.1 118.2 118.3Cooling only Powered off Closed Closed Open mode Heating only Powered onClosed Open Closed mode Cooling plus Powered on Closed Closed Openheating mode Defrosting Powered off Open Closed Closed mode

In Table 1, when the four-way valve 120 is powered on, the thirdinterface 120.3 and the second interface 120.2 of the four-way valve 120are connected, while the first interface 120.1 and the fourth interface120.4 are connected. When the four-way valve 120 is powered off, thethird interface 120.3 and the fourth interface 120.4 of the four-wayvalve 120 are connected, while the first interface 120.1 and the secondinterface 120.2 are connected.

The heat pump unit of the present disclosure is capable of running inthe following modes by connecting two of the three heat exchangers withthe compressor 101 and the throttling device 107 to form the refrigerantcirculation loop, while leaving the third of the heat exchangersconnected in parallel with the one, which is on the low-pressure side,of the two heat exchangers in the refrigerant circulation loop for spareuse and for start in other modes.

Mode 1: Cooling Only

As shown in FIG. 3A and Table 1, if it is desired to run the heat pumpunit in the cooling only mode, controlling, via the control device 230,the four-way valve 120 to power off it such that the third interface120.3 and the fourth interface 120.4 of the four-way valve 120 areconnected while the first interface 120.1 and the second interface 120.2are connected, and controlling, via the control device 230, the thirdvalve 118.3 of the throttling-device-outlet-side control valve group toopen it. The second valve 115.2 of the throttling-device-inlet-sidecontrol valve group can be automatically opened since it is a one-wayvalve. The other valves are closed. In this way, the high-pressurerefrigerant discharged from the exhaust end 105 of the compressor 101first passes through the second heat exchanger 102, then flows throughthe second valve 115.2 of the throttling-device-inlet-side control valvegroup into the inlet end 108 of the throttling device 107 and is changedinto a low-pressure refrigerant, then the low-pressure refrigerant flowsthrough the third valve 118.3 of the throttling-device-outlet-sidecontrol valve group into the third heat exchanger 103, and finally therefrigerant flows from the third heat exchanger 103 to the suction end106 of the compressor 101 to complete the circulation of therefrigerant.

In the cooling only mode, the compressor 101, the throttling device 107,the second heat exchanger 102 and the third heat exchanger 103 are inthe refrigerant circulation loop, the second heat exchanger 102 acts asa condenser, and the third heat exchanger 103 acts as an evaporator andcools externally via the second water supply and return pipe 111.2. Thefirst heat exchanger 104 is for spare use and is connected in parallelwith the third heat exchanger 103, and the first heat exchanger 104 isnot in the refrigerant circulation loop.

Mode 2: Heating Only

As shown in FIG. 3B and Table 1, if it is desired to run the heat pumpunit in the heating only mode, controlling, via the control device 230,the four-way valve 120 to power on it such that the third interface120.3 and the second interface 120.2 of the four-way valve 120 areconnected while the first interface 120.1 and the fourth interface 120.4are connected, and controlling, via the control device 230, the secondvalve 118.2 of the throttling-device-outlet-side control valve group toopen it. The first valve 115.1 of the throttling-device-inlet-sidecontrol valve group can be automatically opened since it is a one-wayvalve. The other valves are closed. In this way, the high-pressurerefrigerant discharged from the exhaust end 105 of the compressor 101first passes through the first heat exchanger 104, then flows throughthe first valve 115.1 of the throttling-device-inlet-side control valvegroup into the inlet end 108 of the throttling device 107 and is changedinto a low-pressure refrigerant, then the low-pressure refrigerant flowsthrough the second valve 118.2 of the throttling-device-outlet-sidecontrol valve group into the second heat exchanger 102, and finally therefrigerant flows from the second heat exchanger 102 to the suction end106 of the compressor 101 to complete the circulation of therefrigerant.

In the heating only mode, the compressor 101, the throttling device 107,the first heat exchanger 104 and the second heat exchanger 102 are inthe refrigerant circulation loop, the first heat exchanger 104 acts as acondenser and heats externally via the first water supply and returnpipe 111.1, and the second heat exchanger 102 acts as an evaporator. Thethird heat exchanger 103 is for spare use and is connected in parallelwith the second heat exchanger 102, and the third heat exchanger 103 isnot in the refrigerant circulation loop.

Mode 3: Cooling Plus Heating

As shown in FIG. 3C and Table 1, if it is desired to run the heat pumpunit in the cooling plus heating mode, controlling, via the controldevice 230, the four-way valve 120 to power on it such that the thirdinterface 120.3 and the second interface 120.2 of the four-way valve 120are connected while the first interface 120.1 and the fourth interface120.4 are connected, and controlling, via the control device 230, thethird valve 118.3 of the throttling-device-outlet-side control valvegroup to open it. The first valve 115.1 of thethrottling-device-inlet-side control valve group can be automaticallyopened since it is a one-way valve. The other valves are closed. In thisway, the high-pressure refrigerant discharged from the exhaust end 105of the compressor 101 first passes through the first heat exchanger 104,then flows through the first valve 115.1 of thethrottling-device-inlet-side control valve group into the inlet end 108of the throttling device 107 and is changed into a low-pressurerefrigerant, then the low-pressure refrigerant flows through the thirdvalve 118.3 of the throttling-device-outlet-side control valve groupinto the third heat exchanger 103, and finally the refrigerant flowsfrom the third heat exchanger 103 to the suction end 106 of thecompressor 101 to complete the circulation of the refrigerant.

In the cooling plus heating mode, the compressor 101, the throttlingdevice 107, the first heat exchanger 104 and the third heat exchanger103 are in the refrigerant circulation loop, the first heat exchanger104 acts as a condenser and heats externally via the first water supplyand return pipe 111.1, and the third heat exchanger 103 acts as anevaporator and cools externally via the second water supply and returnpipe 111.2. The second heat exchanger 102 is for spare use and isconnected in parallel with the third heat exchanger 103, and the secondheat exchanger 102 is not in the refrigerant circulation loop.

Mode 4: Defrosting

When the heat pump unit runs in the heating only mode and the ambienttemperature is low, the surface of the second heat exchanger 102 as anair heat exchanger will be frosted and it is desired to defrost thesurface by heating it.

As shown in FIG. 3D and Table 1, if it is desired to run the heat pumpunit in the defrosting mode, controlling, via the control device 230,the four-way valve 120 to power off it such that the third interface120.3 and the fourth interface 120.4 of the four-way valve 120 areconnected while the first interface 120.1 and the second interface 120.2are connected, and controlling, via the control device 230, the firstvalve 118.1 of the throttling-device-outlet-side control valve group toopen it. The second valve 115.2 of the throttling-device-inlet-sidecontrol valve group can be automatically opened since it is a one-wayvalve. The other valves are closed. In this way, the high-pressurerefrigerant discharged from the exhaust end 105 of the compressor 101first passes through the second heat exchanger 102, then flows throughthe second valve 115.2 of the throttling-device-inlet-side control valvegroup into the inlet end 108 of the throttling device 107 and is changedinto a low-pressure refrigerant, then the low-pressure refrigerant flowsthrough the first valve 118.1 of the throttling-device-outlet-sidecontrol valve group into the first heat exchanger 104, and finally therefrigerant flows from the first heat exchanger 104 to the suction end106 of the compressor 101 to complete the circulation of therefrigerant.

In the defrosting mode, the compressor 101, the throttling device 107,the first heat exchanger 104 and the second heat exchanger 102 are inthe refrigerant circulation loop, the second heat exchanger 102 acts asa condenser and heats externally so that the second heat exchanger 102is defrosted, and the first heat exchanger 104 acts as an evaporator.The third heat exchanger 103 is for spare use and is connected inparallel with the first heat exchanger 104, and the third heat exchanger103 is not in the refrigerant circulation loop.

During the running of the heat pump unit in any of above-mentionedmodes, if the degree of super-cooling of the refrigerant in thecondenser is too high, the corresponding valve 113.1 or 113.2 in themid-pressure tank first inlet control valve group of the heat exchangeracting as the condenser is opened and the redundant refrigerant in theheat exchanger acting as the condenser is discharged into themid-pressure tank 110; if the degree of super-cooling is not too high,the corresponding valve 113.1 or 113.2 in the mid-pressure tank firstinlet control valve group is closed and the discharge of redundantrefrigerant stops. If the pressure in the low-pressure side of therunning heat pump unit is too low, the mid-pressure tank first outletcontrol valve 114 is opened and the refrigerant in the mid-pressure tank110 flows to the low-pressure side of the running system via themid-pressure tank first outlet control valve 114 to supplementrefrigerant; if the pressure is no longer too low, the mid-pressure tankfirst outlet control valve 114 is closed and refrigerant supplementationstops. The closing and opening of the valve 113.1 or 113.2 and the valve114 are controlled by the control device 230.

If the run mode of the heat pump unit is switched among theaforementioned multiple modes, a pressure release operation may bedesired in some situations to the first heat exchanger 104 or the secondheat exchanger 102 which is capable of acting as a condenser.Specifically, when a heat exchanger acting as a condenser in apre-switching run mode does not act as a condenser in a post-switchingrun mode, then it is desired to perform the pressure release operation.

Table 2 is the mode switching table for the heat pump unit of FIG. 1.Whether a pressure release operation is desired during the modeswitching is summarized in Table 2. The activated valves in each modeare also summarized in Table 2. The contents in Table 2 are stored inthe storage 254 as shown in FIG. 2A. The processer 244 can determinewhether it is desired to perform a pressure release operation to thefirst heat exchanger 104 or the second heat exchanger 102 by readingTable 2 after receiving a request of switching the current run mode(i.e., a pre-switching run mode) of the heat pump unit to apost-switching run mode.

TABLE 2 Status of Valves During Switching of Heat Pump Unit ModesActivated valves Activated valves Activated valves Pre-switching in thepre- Post-switching in the post- in the pressure run mode switching runmode run mode switching run mode release operation Cooling 118.3 Heatingonly 120/118.2 113.2 only Cooling plus 120/118.3 113.2 heating Heating120/118.2 Cooling only 118.3 113.1 only Cooling plus 120/118.3 Nopressure heating release operation Defrosting 118.1 113.1 Cooling120/118.3 Cooling only 118.3 113.1 plus heating Heating only 120/118.2No pressure release operation Defrosting 118.1 Heating only 120/118.2113.2

In Table 2, the four-way valve 120 is powered on when it is activatedand the control valves 118.1, 118.2, 118.3, 113.1 and 113.2 are openedwhen they are activated. The specific pressure release operations to theheat exchangers may be described as Operation 1, Operation 2, Operation3, and Operation 4. Each of Operations 1-4 is described in furtherdetail below.

Operation 1 may include fluidly connecting the first heat exchanger 104to the mid-pressure tank first inlet 112 so as to discharge therefrigerant from the first heat exchanger 104 to the mid-pressure tank110. Operation 1 corresponds to opening the valve 113.1 (i.e., the firstvalve 113.1 of the mid-pressure first inlet control valve group) inTable 2.

Operation 2 may include fluidly connecting the second heat exchanger 102to the mid-pressure tank first inlet 112 so as to discharge therefrigerant from the second heat exchanger 102 to the mid-pressure tank110. Operation 2 corresponds to opening the valve 113.2 (i.e., thesecond valve 113.2 of the mid-pressure first inlet control valve group)in Table 2.

As indicated in Table 2, when it is desired to switch the run mode ofthe heat pump unit from the cooling only mode (the pre-switching runmode) to the heating only mode or the cooling plus heating mode (thepost-switching run mode), it is desired to perform the pressure releaseoperation to the second heat exchanger 102 since the second heatexchanger 102 acting as a condenser in the cooling only mode does notact as a condenser in the heating only mode or the cooling plus heatingmode. The desired pressure release operation to the second heatexchanger 102 is Operation 2.

When it is desired to switch the run mode of the heat pump unit from theheating only mode (the pre-switching run mode) to the cooling only modeor the defrosting mode (the post-switching run mode), it is desired toperform the pressure release operation to the first heat exchanger 104since the first heat exchanger 104 acting as a condenser in the heatingonly mode does not act as a condenser in the cooling only mode or thedefrosting mode. The desired pressure release operation to the firstheat exchanger 104 is Operation 1.

When it is desired to switch the run mode of the heat pump unit from thecooling plus heating mode (the pre-switching run mode) to the coolingonly mode (the post-switching run mode), it is desired to perform thepressure release operation to the first heat exchanger 104 since thefirst heat exchanger 104 acting as a condenser in the cooling plusheating mode does not act as a condenser in the cooling only mode. Thedesired pressure release operation to the first heat exchanger 104 isOperation 1.

When it is desired to switch the run mode of the heat pump unit from thedefrosting mode (the pre-switching run mode) to the heating only mode(the post-switching run mode), it is desired to perform the pressurerelease operation to the second heat exchanger 102 since the second heatexchanger 102 acting as a condenser in the defrosting mode does not actas a condenser in the heating only mode. The desired pressure releaseoperation to the second heat exchanger 102 is Operation 2.

Still as indicated in Table 2, when it is desired to switch the run modeof the heat pump unit between the heating only mode and the cooling plusheating mode, no pressure release operation is desired since the firstheat exchanger 104 acts as a condenser in both of the two modes.

Referring now to FIG. 4, a process flow diagram illustrating a method400 of switching the run mode for the heat pump unit of FIG. 1 isdepicted. The steps of the method 400 as shown are stored in the storage254 of the control device 230 and performed by the control device 230.

Process 400 may commence with step 450. Step 450 may include receiving amode switching request, namely a request for switching the run mode ofthe heat pump unit from the pre-switching run mode to the post-switchingrun mode. The control device 230 receives the mode switching request viathe input interface 248. The mode switching request is, for example,inputted by an operator via a user interface connecting to the inputinterface 248, or automatically sent from the heat pump unit accordingto the operation parameters.

Process 400 may continue with step 451. Step may include determiningwhether it is desired to perform the pressure release operation to thefirst heat exchanger 104 or the second heat exchanger 102. The controldevice 230 determines, according to Table 2 stored in the storage 254,whether it is desired to perform the pressure release operation to thefirst heat exchanger 104 or the second heat exchanger 102 if the runmode of the heat pump unit is to be switched from the pre-switching runmode to the requested post-switching run mode. The control device 230turns to Step 4521 if it is determined that it is desired to perform thepressure release operation to the first heat exchanger 104, turns toStep 4522 if it is determined that it is desired to perform the pressurerelease operation to the second heat exchanger 102, and turns to Step460 if it is determined that no pressure release operation is desired tothe first heat exchanger 104 or the second heat exchanger 102.

Step 4521 may include performing the aforementioned Operation 1 and thenturning to Step 4531. By performing Operation 1, the first valve 113.1of the mid-pressure first inlet control valve group is opened such thatthe first heat exchanger 104 is fluidly connected to the mid-pressurefirst inlet 112 to discharge the refrigerant in the first heat exchanger104 into the mid-pressure tank 110.

Step 4522 may include performing the aforementioned Operation 2 and thenturning to Step 4532. By performing Operation 2, the second valve 113.2of the mid-pressure first inlet control valve group is opened such thatthe second heat exchanger 102 is fluidly connected to the mid-pressurefirst inlet 112 to discharge the refrigerant in the second heatexchanger 102 into the mid-pressure tank 110.

Step 4531 may include determining whether a first predetermined amountof time has elapsed since Operation 1 is performed. If yes, it isconsidered that the pressure release operation may be ended and thecontrol device 230 turns to Step 4581. If not, the control device 230continues to perform Step 4531 until it is determined that the firstpredetermined amount of time has elapsed. The first predetermined amountof time can be determined according to the cooling capacity/heatingcapacity of the heat pump unit. As an example, the first predeterminedamount of time is about 30-60 seconds.

Step 4532 may include determining whether a second predetermined amountof time has elapsed since Operation 2 is performed. If yes, it isconsidered that the pressure release operation may be ended and thecontrol device 230 turns to Step 4582. If not, the control device 230continues to perform Step 4532 until it is determined that the secondpredetermined amount of time has elapsed. The second predeterminedamount of time can be also determined according to the coolingcapacity/heating capacity of the heat pump unit. As an example, thesecond predetermined amount of time is about 30-60 seconds. The secondpredetermined amount of time can be the same as or different from thefirst predetermined amount of time.

Step 4581 may include performing Operation 3, namely, disconnecting thefirst heat exchanger 104 from the mid-pressure first inlet 112, and thenturning to Step 460. Operation 3 corresponds to closing the valve 113.1(i.e., the first valve 113.1 of the mid-pressure first inlet controlvalve group).

Step 4582 may include performing Operation 4, namely, disconnecting thesecond heat exchanger 102 from the mid-pressure first inlet 112, andthen turning to Step 460. Operation 4 corresponds to closing the valve113.2 (i.e., the second valve 113.2 of the mid-pressure first inletcontrol valve group).

Process 400 may conclude with step 460. Step 460 may include startingthe post-switching run mode and ending the pre-switching run mode tofinish the mode switching. In Step 460, the post-switching run mode isstarted by activating the corresponding valves which may be activated inthe post-switching run mode. The valves to be activated for each kind ofpost-switching run mode are summarized in Table 2. Specifically, thevalve 120 (i.e., the four-way valve 120) and the valve 118.2 (i.e., thesecond valve 118.2 of the throttling-device-outlet-side control valvegroup) will be activated if the post-switching run mode is the heatingonly mode, the valve 118.3 (i.e., the third valve 118.3 of thethrottling-device-outlet-side control valve group) will be activated ifthe post-switching run mode is the cooling only mode, the valve 120(i.e., the four-way valve 120) and the valve 118.3 (i.e., the thirdvalve 118.3 of the throttling-device-outlet-side control valve group)will be activated if the post-switching run mode is the cooling plusheating mode, and the valve 118.1 (i.e., the first valve 118.1 of thethrottling-device-outlet-side control valve group) will be activated ifthe post-switching run mode is the defrosting mode.

In Step 460, the pre-switching run mode is ended by deactivating thecorresponding valves which are activated in the pre-switching run mode.The valves activated for each kind of pre-switching run mode aresummarized in Table 2. Specifically, the valve 120 and the valve 118.2will be deactivated if the pre-switching run mode is the heating onlymode, and the valve 118.3 will be deactivated if the pre-switching runmode is the cooling only mode, the valve 120 and the valve 118.3 will bedeactivated if the pre-switching run mode is the cooling plus heatingmode, and the valve 118.1 will be activated if the pre-switching runmode is the defrosting mode.

It should be noted that even though starting the post-switching run modeand ending the pre-switching run mode are performed in the same Step460, the pre-switching run mode can be ended after a certain time delayfrom starting the post-switching run mode in other embodiments accordingto the present disclosure.

According to the present disclosure, the control device 230 is furtherconfigured to perform Operation 5, namely, fluidly connecting themid-pressure tank first outlet 128 and the outlet end 109 of thethrottling device 107, if it is desired to supplement refrigerant to therefrigerant circulation loop of the post-switching run mode after thepost-switching run mode is started. Operation 5 corresponds to openingthe mid-pressure tank first outlet control valve 114. The control device230 is further configured to fluidly connecting the mid-pressure secondinlet 181 to the exhaust end 105 of the compressor 101 by opening themid-pressure tank pressure-increasing control valve 135 if the pressuresensor 161 detects that the pressure in the mid-pressure tank 110 isbelow a first predetermined pressure value during performing Operation5. In this way, the pressure in the mid-pressure tank 110 can beincreased to ensure that the refrigerant in the mid-pressure tank 110can be supplemented into the refrigerant circulation loop. As anexample, the control device 230 is configured to close the mid-pressuretank pressure-increasing control valve 135 if the pressure in themid-pressure tank 110 is increased above the pressure at themid-pressure first outlet 128.

According to the present disclosure, the control device 230 is furtherconfigured to fluidly connecting the mid-pressure tank second outlet 182to the suction end 106 of the compressor 101 by opening the mid-pressuretank pressure-reducing control valve 136 if the pressure sensor 161detects that the pressure in the mid-pressure tank 110 is above a secondpredetermined pressure value during performing Operation 1 or Operation2. In this way, the pressure in the mid-pressure tank 110 can be reducedto ensure that the high-pressure refrigerant in the first heat exchanger104 or the second heat exchanger 102 can be discharged into themid-pressure tank 110. As an example, the control device 230 isconfigured to close the mid-pressure tank pressure-reducing controlvalve 136 if the pressure in the mid-pressure tank 110 is reduced belowthe pressure at the mid-pressure first inlet 112.

The aforementioned first predetermined pressure value and secondpredetermined pressure value can be determined according to the desiredrange of value for the pressure in the mid-pressure tank 110.

Furthermore, according to the present disclosure, to further ensure theeffectiveness of the mode switching, the control device 230 is furtherconfigured to determine whether the pressure in the heat exchanger towhich the pressure release operation has been performed is still high bydetecting the pressure of the refrigerant in the heat exchanger with thecorresponding pressure sensor 164/162. If yes, it is considered that themode switching fails and then the control device 230 stops the heat pumpunit.

FIG. 5A illustrates the flow path of the refrigerant when switching therun mode of the heat pump unit of FIG. 1 from the cooling only mode tothe cooling plus heating mode. The following describes how to releasepressure from the heat exchanger that needs pressure release by takingsome of the operations for switching the run mode of the heat pump unitfrom the cooling only mode to the cooling plus heating mode as anexample.

If the run mode of the heat pump unit is to be switched from the coolingonly mode as shown in FIG. 3A to the cooling plus heating mode as shownin FIG. 3C, the second heat exchanger 102 will be switched from the heatexchanger acting as a condenser on the high-pressure side to a spareheat exchanger, and therefore pressure release is desired to the secondheat exchanger 102.

As shown in FIG. 5A, when the heat pump unit is still running in thecooling only mode, the second valve 113.2 of the mid-pressure tank firstinlet control valve group is first opened to fluidly connect the secondheat exchanger 102 to the mid-pressure tank first inlet 112 so that thehigh-pressure refrigerant in the second heat exchanger 102 can bedischarged into the mid-pressure tank 110.

The pressure release operation to the second heat exchanger 102 as shownin FIG. 5A will be ended after the second predetermined amount of timehas elapsed. To end the pressure release operation, the second valve113.2 of the mid-pressure tank first inlet control valve group will beclosed to disconnect the second port 121.2 of the second heat exchanger102 from the mid-pressure tank first inlet 112. After that, the run modewill be switched from the cooling only mode to the cooling plus heatingmode by controlling the four-way valve 120 to power on it, so as toconnect the third interface 120.3 and the second interface 120.2 of thefour-way valve 120 and connect the fourth interface 120.4 and the firstinterface 120.1. Since the third valve 118.3 of thethrottling-device-outlet-side control valve group is opened in both ofthe cooling only mode and the cooling plus heating mode, the switchingto the cooling plus heating mode can be completed without any operationto the third valve 118.3.

FIG. 5B illustrates the flow path of the refrigerant when performingrefrigerant supplement operation to the refrigerant circulation loop ofthe heat pump unit of FIG. 1 running in the cooling plus heating mode.

The refrigerant circulation loop of the heat pump unit may need therefrigerant supplement operation when it is normally running in the fourmodes. For example, after the run mode of the heat pump unit is switchedfrom the cooling only mode as shown in FIG. 5A to the cooling plusheating mode as shown in FIG. 5B, the refrigerant circulation loop inthe cooling plus heating mode may need refrigerant supplement due to thepressure release operation as shown in FIG. 5A. To this end, as shown inFIG. 5B, the mid-pressure first outlet control valve 114 is opened tofluidly connect the mid-pressure first outlet 128 to the outlet end 109of the throttling device 107 so that the refrigerant in the mid-pressuretank 110 can be supplemented into the refrigerant circulation loop. Inthe meantime, if the pressure in the mid-pressure tank 110 is notenough, the mid-pressure tank pressure-increasing control valve 135 isopened to fluidly connect the mid-pressure second inlet 181 to theexhaust end 105 of the compressor 101 so as to increase the pressure inthe mid-pressure tank 110 to ensure that the refrigerant in themid-pressure tank 110 can be supplemented into the refrigerantcirculation loop.

By performing the pressure release operation to the heat exchanger whichneeds the operation during mode switching, on the one hand, the pressureshock caused when the heat exchanger on the high-pressure side isswitched to be a heat exchanger on the low-pressure side at the time ofmode switching can be prevented, and on the other hand, the residualliquid refrigerant in the heat exchanger on the high-pressure side isnot enough to be brought from the suction end into the compressor tocause a liquid shock after mode switching. Furthermore, by performingthe mode switching method of the present disclosure, on the one hand,since the pressure difference during pressure release is very small, thevibration intensity during pressure release is also very small, and onthe other hand, the switching time is very short and the correspondingshock force is also small. Therefore, this switching process can beconsidered smoother and more efficient than a conventional shutdownswitching process.

As an example, if it is desired to switch the run modes, the load of thecompressor 101 can first be reduced so that the refrigerantparticipating in the refrigerant circulation of the heat pump unit isreduced, and the refrigerant can be discharged into the mid-pressuretank 110 as much as possible. In addition, by reducing the suctionvolume and discharge volume of the compressor, the corresponding shockforce at the time of mode switching will also be very small.

In addition, through the receiving and supplementing of the refrigerantby the mid-pressure tank 110, the shock caused by a pressure jump at thetime of mode switching on the heat pump unit can be reduced, the servicelives of the components can be prolonged, and the running reliabilityand stability of the heat pump unit can be improved. In addition,through the reasonable control of the refrigerant in the refrigerantcirculation loop of the heat pump unit running in a normal run mode bythe mid-pressure tank 110, the reliability and the energy efficiencyratio of the heat pump unit can be improved.

FIG. 6 is a block diagram of the heat pump unit according to anotherembodiment of the present application. To further improve the energyefficiency ratio and the running stability of the heat pump unit, theembodiment of the heat pump unit as shown in FIG. 6 is provided. Theembodiment as shown in FIG. 6 includes all the components in FIG. 1 andis further provided with an oil separator 630, a drying filter 632 andan economizer 634 based on the heat pump unit of FIG. 1.

As shown in FIG. 6, the oil separator 630 is located between the exhaustend 105 of the compressor 101 and the four-way valve 120 and isconfigured to separate the oil discharged from the compressor 101. Thedrying filter 632 is located at the upstream side of the inlet end 108of the throttling device 107 and the drying filter 632 is configured todry and filter the high-pressure refrigerant before the high-pressurerefrigerant flows into the throttling device 107. The economizer 634 islocated at the downstream side of the drying filter 632. The outlet ofthe drying filter 632 is connected to the liquid inlet on thesuper-cooling side of the economizer 634, the liquid outlet on thesuper-cooling side of the economizer 634 is connected to the inlet end108 of the throttling device 107, and the gas outlet of the economizer634 is connected to the gas replenishing port of the compressor 101.Thus, the degree of super-cooling of the system, the gas deliverycapacity, and the performance of the heat pump unit can further beimproved.

Although the present disclosure is described by reference to thespecific implementation modes shown in the drawings, it should beunderstood that the heat pump unit in the present disclosure can havemany variants, without departing from the spirit, scope and backgroundof the present application. Those skilled in the art should also realizethat different changes to the structural details in the embodimentsdisclosed in the present application should all fall within the spiritand scope of the present application and the claims.

1. A heat pump unit, comprising: a compressor having a suction end andan exhaust end; a throttling device having an inlet end and an outletend; a first heat exchanger, a second heat exchanger and a third heatexchanger, the first heat exchanger having a first port and a secondport, the second heat exchanger having a first port and a second port,and the third heat exchanger having a first port and a second port; anda mid-pressure tank being provided with a mid-pressure tank first inlet;wherein the first port of the first heat exchanger and the first port ofthe second heat exchanger are controllably fluidly connected to thesuction end of the compressor, and controllably fluidly connected to theexhaust end of the compressor, and wherein the first port of the thirdheat exchanger is fluidly connected to the suction end of thecompressor; and wherein the second port of the first heat exchanger andthe second port of the second heat exchanger are controllably fluidlyconnected to the inlet end of the throttling device, controllablyfluidly connected to the outlet end of the throttling device, andcontrollably fluidly connected to the mid-pressure tank first inlet, andwherein the second port of the third heat exchanger is controllablyfluidly connected to the outlet end of the throttling device.
 2. Theheat pump unit of claim 1, further comprising: a four-way valve having afirst interface, a second interface, a third interface, and a fourthinterface; wherein the first port of the first heat exchanger isconnected to the second interface of the four-way valve, the first portof the second heat exchanger is connected to the fourth interface of thefour-way valve, the suction end of the compressor is connected to thefirst interface of the four-way valve and the exhaust end of thecompressor is connected to the third interface of the four-way valve. 3.The heat pump unit of claim 2, further comprising: athrottling-device-inlet-side control valve group including a first valveand a second valve, wherein the second port of the first heat exchangerand the second port of the second heat exchanger are controllablyfluidly connected to the inlet end of the throttling device via thefirst valve and the second valve of the throttling-device-inlet-sidecontrol valve group, respectively; and a throttling-device-outlet-sidecontrol valve group including a first valve, a second valve and a thirdvalve, wherein the second port of the first heat exchanger and thesecond port of the second heat exchanger are controllably fluidlyconnected to the outlet end of the throttling device via the first valveand the second valve of the throttling-device-outlet-side control valvegroup, respectively, and wherein the second port of the third heatexchanger is controllably fluidly connected to the outlet end of thethrottling device via the third valve of thethrottling-device-outlet-side control valve group.
 4. The heat pump unitof claim 3, wherein: the mid-pressure tank is provided with amid-pressure tank first outlet, the mid-pressure tank first outlet iscontrollably fluidly connected to the outlet end of the throttlingdevice; and the heat pump unit further comprises: a mid-pressure tankfirst inlet control valve group comprising a first valve and a secondvalve, wherein the second port of the first heat exchanger and thesecond port of the second heat exchanger are controllably fluidlyconnected to the mid-pressure tank first inlet via the first valve andthe second valve of the mid-pressure tank first inlet control valvegroup, respectively; and a mid-pressure tank first outlet control valvewherein the mid-pressure tank first outlet is controllably fluidlyconnected to the outlet end of the throttling device via themid-pressure tank first outlet control valve.
 5. The heat pump unit ofclaim 4, further comprising: a mid-pressure tank pressure-increasingcontrol valve and a mid-pressure tank pressure-reducing control valve;wherein the mid-pressure tank is provided with a mid-pressure tanksecond inlet and a mid-pressure tank second outlet; and wherein themid-pressure tank second inlet is connected to the fluid path betweenthe exhaust end of the compressor and the four-way valve via themid-pressure tank pressure-increasing control valve, and themid-pressure tank second outlet is connected to the suction end of thecompressor via the mid-pressure tank pressure-reducing control valve. 6.The heat pump unit of claim 4, wherein the mid-pressure tank first inletcontrol valve group further comprises a first one-way valve and a secondone-way valve, wherein the first one-way valve is connected between thefirst valve of the mid-pressure tank first inlet control valve group andthe mid-pressure tank first inlet, and the second one-way valve isconnected between the second valve of the mid-pressure tank first inletcontrol valve group and the mid-pressure tank first inlet.
 7. The heatpump unit of claim 5, wherein the first valve and the second valve ofthe throttling-device-inlet-side control valve group are one-way valves.8. The heat pump unit of claim 7, further comprising a control devicewherein the four-way valve the throttling-device-outlet-side controlvalve group, the mid-pressure tank first inlet control valve group, themid-pressure tank first outlet control valve, the mid-pressure tankpressure-increasing control valve and the mid-pressure tankpressure-reducing control valve are connected to and controlled by thecontrol device.
 9. The heat pump unit of claim 1, wherein the first heatexchanger and the third heat exchanger are connected to a first watersupply and return pipe and a second water supply and return pipe,respectively.
 10. The heat pump unit of claim 1, wherein: the heat pumpunit is configured such that said heat pump unit is capable of runningin multiple modes and being switched between the multiple modes bycontrolling the flow path of the refrigerant through the compressor, thethrottling device, the first heat exchanger, the second heat exchangerand the third heat exchanger; and the high-pressure refrigerant from anyof the first heat exchanger and the second heat exchanger which needspressure release at the time of mode switching can be received by themid-pressure tank.
 11. A method for controlling a heat pump unit, theheat pump unit comprising a compressor, a throttling device, a firstheat exchanger, a second heat exchanger, a third heat exchanger, and amid-pressure tank wherein the heat pump unit is capable of running inmultiple modes and the first heat exchanger or the second heat exchangeris capable of acting as a condenser in the multiple modes, the methodcomprising: determining whether it is desired to perform a pressurerelease operation to the first heat exchanger or the second heatexchanger when it is desired to switch the run mode of the heat pumpunit from a pre-switching run mode to a post-switching run mode; andmaintaining the pre-switching run mode and performing a first operationresponsive to a determination that it is desired to perform the pressurerelease operation to the first heat exchanger, wherein the firstoperation comprises fluidly connecting the first heat exchanger to afirst inlet of the mid-pressure tank so as to discharge the refrigerantfrom the first heat exchanger to the mid-pressure tank; or maintainingthe pre-switching run mode and performing a second operation responsiveto a determination that it is desired to perform the pressure releaseoperation to the second heat exchanger, wherein the second operationcomprises fluidly connecting the second heat exchanger to the firstinlet of the mid-pressure tank so as to discharge the refrigerant fromthe second heat exchanger to the mid-pressure tank.
 12. The method ofclaim 11, further comprising: performing a third operation, wherein thethird operation comprises disconnecting the first heat exchanger fromthe first inlet of the mid-pressure tank after a first predeterminedamount of time has elapsed since the first operation is performed; orperforming a fourth operation, wherein the fourth operation comprisesdisconnecting the second heat exchanger from the first inlet of themid-pressure tank after a second predetermined amount of time haselapsed since the second operation is performed.
 13. The method of claim12, further comprising starting the post-switching run mode and endingthe pre-switching run mode after the third operation or the fourthoperation is performed.
 14. The method of claim 11, further comprising:Performing a fifth operation responsive to a determination that it isdesired to supplement refrigerant to the refrigerant circulation loop ofthe post-switching run mode after the post-switching run mode isstarted, wherein the fifth operation comprises fluidly connecting afirst outlet of the mid-pressure tank to an outlet end of the throttlingdevice.
 15. The method of claim 14, further comprising: fluidlyconnecting a second inlet of the mid-pressure tank to an exhaust end ofthe compressor so as to increase the pressure in the mid-pressure tankresponsive to a determination that the pressure in the mid-pressure tankis below a first predetermined pressure value during the fifthoperation.
 16. The method of claim 11, further comprising: fluidlyconnecting a second outlet of the mid-pressure tank to a suction end ofthe compressor so as to reduce the pressure in the mid-pressure tankresponsive to a determination that the pressure in the mid-pressure tankis above a second predetermined pressure value during the firstoperation or the second operation.
 17. The method of claim 11, whereinthe step of determining whether it is desired to perform a pressurerelease operation to the first heat exchanger or the second heatexchanger comprises: determining that it is desired to perform thepressure release operation to the first heat exchanger or the secondheat exchanger when the first heat exchanger or the second heatexchanger acting as a condenser in the pre-switching run mode does notact as a condenser in the post-switching run mode.
 18. The method ofclaim 17, wherein: the multiple modes comprise a cooling only mode, aheating only mode, a cooling plus heating mode, and a defrosting mode;and the first heat exchanger and the third heat exchanger are connectedto a first water supply and return pipe and a second water supply andreturn pipe, respectively.
 19. The method of claim 18, wherein: thecompressor, the throttling device, the second heat exchanger and thethird heat exchanger are in a refrigerant circulation loop when the heatpump unit runs in the cooling only mode, wherein the second heatexchanger acts as a condenser in the cooling only mode; the compressor,the throttling device, the first heat exchanger and the second heatexchanger are in a refrigerant circulation loop when the heat pump unitruns in the heating only mode, wherein the first heat exchanger acts asa condenser in the heating only mode; the compressor, the throttlingdevice, the first heat exchanger and the third heat exchanger are in arefrigerant circulation loop when the heat pump unit runs in the coolingplus heating mode, wherein the first heat exchanger acts as a condenserin the cooling plus heating mode; and the compressor, the throttlingdevice, the first heat exchanger and the second heat exchanger are in arefrigerant circulation loop when the heat pump unit runs in thedefrosting mode, wherein the second heat exchanger acts as a condenserin the defrosting mode.
 20. The method of claim 19, wherein determiningwhether it is desired to perform a pressure release operation to thefirst heat exchanger or the second heat exchanger comprises: determiningthat it is desired to perform the pressure release operation to thesecond heat exchanger when the pre-switching run mode is the coolingonly mode while the post-switching run mode is the heating only mode orthe cooling plus heating mode; determining that it is desired to performthe pressure release operation to the first heat exchanger when thepre-switching run mode is the heating only mode while the post-switchingrun mode is the cooling only mode or the defrosting mode; determiningthat it is desired to perform the pressure release operation to thefirst heat exchanger when the pre-switching run mode is the cooling plusheating mode while the post-switching run mode is the cooling only mode;or determining that it is desired to perform the pressure releaseoperation to the second heat exchanger when the pre-switching run modeis the defrosting mode while the post-switching run mode is the heatingonly mode.